In recent years, there have been begun studies on a suspension system for a vehicle as disclosed in patent literatures as identified below, specifically, a system including a displacement force generator which includes an electromagnetic motor and which is provided in parallel with a suspension spring and a hydraulic damper. The displacement force generator is configured to generate, based on a force generated by the electromagnetic motor, a displacement force causing the sprung and unsprung portions to be displaced toward or away from each other, in a manner that enables the generated displacement force to be controllable. In this system, the generated displacement force is caused to act as a roll restraining force for restraining roll of a body of the vehicle, thereby making it possible to restrain the roll of the vehicle body.    [Patent Literature 1] JP-2002-218778A    [Patent Literature 2] JP-2002-211224A    [Patent Literature 3] JP-2006-82751A